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' 


A  Contribution  to  the  Investigation  o<  the 
Temperature  Coefficient  of  Osmotic  Pressure;  a 
Redetermination  of  the  Osmotic  Pressures  of  Cane 
Sugar  Solutions  a 


DISSERTATION 

SUBMITTED  TO  THE 

Board  of  University  Studies  of  Johns 
Hopkins  University 

IN  CONFORMITY  WITH  A  REQUIREMENT  FOR  THE  DEGREE  OF 

DOCTOR    OF    PHILOSOPHY 


BY 


WILLIAM  MANSFIELD  CLARK 


B  A  L  T  I  M  ()  R  1- 

1910 


A  Contribution  to  the  Investigation  of  the 
Temperature  Coefficient  of  Osmotic  Pressure;  a 
Redetermination  of  the  Osmotic  Pressures  of  Cane 
Sugar  Solutions  at  20°  &  &  &  &  &  &  & 


DISSERTATION 

SUBMITTED  TO  THE 

Board  of  University  Studies  of  Johns 
Hopkins  University 

IN  CONFORMITY  WITH  A  REQUIREMENT  FOR  THE  DEGREE  OF 

DOCTOR    OF    PHILOSOPHY 


BY 


WILLIAM  MANSFIELD  CLARK 


BALTIMORE 
1910 


CONTENTS. 

Page. 

Acknowledgment 3 

Preface 4 

Purification  and  Analysis  of  the  Cane  Sugar.  . 5 

Improvements  in  Apparatus 9 

The  Measurements: 

Preliminary  Discussion i  I 

Tables 17 

Discussions  of  Results   1 19 

Theoretical   Considerations 27 

Summary    30 

Biography    31 


ACKNOWLEDGMENT. 

This  investigation  was  carried  out  under  the  supervision  of 
Professor  Morse,  to  whom  the  author  wishes  to  express  his 
gratitude  for  instruction  in  lecture  room  and  laboratory.  The 
measurements  of  osmotic  pressures  were  made  in  collaboration 
with  Dr.  Zeis,  Dr.  Holland,  Mr.  Carpenter  and  Mr.  Meyers, 
and  special  credit  is  due  Dr.  Zeis,  who  was  in  charge  of  the 
measurements  from  Oct.  i  to  March  i. 

I  desire  to  thank  Dr.  Turner  and  Dr.  Pfund  for  helpful 
suggestions,  and  to  express  my  obligation  to  President  Remsen, 
Professor  Jones,  Professor  Acree,  Professor  Bliss  and  Dr. 
Pfund  for  instruction. 


239378 


PREFACE. 

The  investigation  here  recorded  was  a  study  of  the  osmotic 
pressures  of  cane  sugar  solutions  at  20°.  It  is  one  of  a  series 
of  investigations  having  for  their  object  the  establishment  of 
the  temperature  coefficient  of  the  osmotic  pressures  of  cane 
sugar  solutions,  ranging  in  concentration  from  one-tenth 
weight1  normal,  to  normal  at  intervals  of  5°  between  o°  and 
25°-30°. 

Those  phases  of  the  subject  which  are  dealt  with  in  this 
paper  are : 

1.  Purification  and  analysis  of  the  cane  sugar. 

2.  Improvements  in  apparatus. 

3.  The  measurements  at  20°  and  their  discussion. 


1  Morse,  Frazer  and  Dunbar,  Am.   Chem.  J.,  38,  2,  '07. 


PURIFICATION  AND  ANALYSIS  OF  THE  CANE 

SUGAR. 

The  methods  in  use  at  this  laboratory  for  measuring  osmotic 
pressures  having  reached  a  high  state  of  accuracy  it  became 
desirable  to  make  the  measurements  with  a  single  stock  of 
sugar  of  known  purity.  Previously,  while  the  methods  were 
in  a  less  satisfactory  state,  the  sugar  used  was  the  purest 
obtainable  commercial  rock  candy,  the  uniformity  of  which  was 
only  assured  within  certain  limits. 

The  method  of  purification  employed  was  essentially  that 
described  by  Cohen  and  Commelin1.  The  original  material 
was  a  rock  candy  crystalized  by  a  local  firm.  This  was  ground 
in  a  porcelain  mortar,  and  dissolved  in  previously  boiled,  dis- 
tilled water,  warmed  in  a  porcelain  dish  over  a  water  bath  for 
not  longer  than  twenty  minutes,  and  at  a  temperature  never 
allowed  to  exceed  60°.  When  approximate  saturation  was 
obtained  in  this  manner,  the  solution  was  quickly  filtered  with 
suction,  and  precipitated  with  98%  ethyl  alcohol,  which  had 
previously  been  distilled  from  lime  through  a  column  of  beads. 
Samples  of  this  alcohol  were  tested  from  time  to  time  and 
found  free  of  lime.  The  precipitated  sugar  was  filtered  with 
suction,  and,  after  draining  three  to  six  hours,  was  washed 
with  85%  ethyl  alcohol.  To  make  the  washing  the  more 
thorough,  the  sugar  was  each  time  removed  from  the  funnel, 
and  stirred  vigorously  with  the  alcohol.  Thirty-two  kilo  lots 
of  the  sugar  at  this  stage  were  very  carefully  mixed,  and  then 
in  small  lots  again  subjected  to  the  same  process  of  purification. 
In  addition  to  the  washing  with  ethyl,  hot  methyl  alcohol  was 
used  for  the  final  washing.  The  separate  precipitates  were 
then  thoroughly  mixed  with  each  other,  dried  at  60°,  and  bot- 
tled after  another  thorough  mixing.  Sixteen  kilograms  of  this 
twice  precipitated  sugar  constitutes  the  supply  which  has  been 
drawn  upon  for  all  measurements  since  March  26th,  1909. 
Previously,  since  January  ist,  a  smaller  sample  of  three  times 
precipitated  sugar  had  been  used.  A  large  portion  of  the  stock 
has  been  kept  over  calcium  chlorid  to  insure  desiccation  and 
the  removal  of  alcohol  before  use. 

In  the  following  analyses  "Sample  A"  designates  the  original 
rock  candy,  B  the  once  precipitated,  C  the  twice  precipitated, 
and  D  a  small  preliminary  batch  which  was  carried  through 
three  precipitations. 

IZt.   Phys.   Chem.,  64,  1. 


Combustion  With  Electric  Furnace. 
SAMPLE  A.  SAMPLE  B. 


6.432 ...42.156 

(6.506 42.335)1 

6.495 42.081 

6.477...        ...42.090 


6.488 
6.482 

.006 


42.109 
42.083 

+  .026 


6.430 42.116 

6.451 42.059 

6.465....      42.151 


6.445 
6.482 

—  .037 


42.108       Average 
42.083    Theoretical 

+  .025     Difference 


SAMPLE  C. 


6.466 42.151 

6.420 42.081 

6.471...  ...42.116 


6.452 
6.482 

—  .030 


42.116 
42.083 

+  .033 


SAMPLE  D. 


6.484 42.047 

6.410 42.104 

6.453 42.009 

6.487 42.031 

6.485....  ...42.101 


6.464 
6.482 

—  .018 


42.058 
42.083 


Average 
Theoretical 


—  025     Difference 


1  Not  averaged,  although  no  error  in  the  determination  was  detected. 

Ash. 

A  large  known  weight  of  each  sample  was  incinerated  in  a 
platinum  crucible  protected  from  the  free  flame  by  a  porcelain 
dish.  All  samples  showed  an  ash  content  of  from  21  to  50 
parts  per  million.  Each  residue  gave  a  test  for  iron,  although 
the  sugar  came  into  contact  with  iron  at  no  time  during  the 
process  of  purification.  In  order  to  make  sure  that  no  contam- 
ination by  the  lime  used  in  concentrating  the  alcohol  had  oc- 
curred, thirty-five  grams  of  Sample  C  were  charred,  and  partly 
incinerated  to  reduce  its  volume,  and  a  spectroscopic  examina- 
tion for  Ca  was  made  with  the  electric  arc  and  a  Roland  grat- 
ing, and  again  with  the  Bunsen  flame  and  a  prism  spectroscope. 
Duplicate  examinations  with  different  incinerated  samples  were 
made  in  each  case.  In  no  case  was  a  trace  of  a  calcium  line 
discovered  by  visual  or  photographic  exploration  in  the  visual 
region  of  the  spectra.  Dr.  Pfund,  of  the  Department  of 
Physics,  who  made  the  examination  with  the  Roland  grating, 
then  photographed  for  the  brilliant  H  and  K  lines  of  the  ultra 
violet,  and  found  them  only  in  about  the  same  intensity  as  in  the 
photograph  with  the  comparate  blank  carbons. 


Reducing  Sugars. 

Analyses  for  reducing  sugars  were  made  in  accordance  with 
the  directions  described  in*  Methods  of  Analysis  Adopted  by 
the  Association  of  Official  Agricultural  Chemists*  "for  mate- 
rials containing  i%  or  less  of  invert  sugar  and  a  high  percent- 
age of  sucrose."  Since  the  precipitate  in  each  case  contained 
considerably  less  than  50  milligrams  of  copper,  the  lowest 
figure  for  copper  in  Hertzf eld's  table,  and  since  there  is  no 
statement  either  of  the  method  of  extrapolation  or  of  the 
standard  sugar  used  in  preparing  this  table,  the  method  was 
abandoned  for  that  of  Soldaini  as  modified  by  Ost.2  Prelim- 
inary experiments  with  aliquot  portions  of  known  glucose 
solution  gave, 

i.  0.0089  g  taken  2.  0.0089  g  taken 

0.0088  g  found  0.0089  g  found 

Using  10  g.  portions  of  each  sample  the  following  data 
were  obtained.  Ost's  table  for  conversion  of  Cu  to  the  equiv- 
alent of  invert  sugar  formed  the  basis  of  the  calculations :  ;i 

Grams  Cu.  Grams  invert        %of  invert  sugar        Sample 

found.  sugar  calculated.          in  sample. 

0.0277 0.0081 

00280 0.0082 

0.0293 0.0085 

0.0283...  ....0.0083 


0.0083  0.083?; 


0.0100 0.0017 

0.0137 0.0019 

0.0142 0.0018 

0.0018  0.018^  B 

0.0085 0.0017  less  than 

0.0108 0.0018 

0.0106 0.0017 

0.0062 0.0017  less  than 

less  than  0.0017  less  than  0.017^  C 

0.0065  0.0017  less  than  .    ,    .,.^ 

less  than  0.0017  less  then  0.017^  D1 

xOnly  one  analysis  of  D  made  because  of  low  supply. 

According  to  these  analyses,  a  normal  solution  of  Sample  C 
would  be  about  ^  with  respect  to  invert  sugar.  If  we 
assume  that  one  molecule  of  invert  sugar  takes  the  place  of  one 

1  Bulletin  4G,  U.  S.   Dept.   Agriculture. 

2  Wiley;   Practice  of   Agricultural   Chemistry,   Vol.    III. 


8 

molecule  of  sucrose,  and  that  the  second  molecule  of  the  two, 
which  together  approximate  the  weight  of  one  molecule  of 
sucrose,  is  the  only  one  which  would  produce  an  error  in  the 
osmotic  pressure,  then  we  may  say  that  a  normal  solution  of 
Sample  C  would  have  a  true  normality  of  approximately  I-f-gjfr. 
A  further  striking  qualitative  difference  between  the  original  and 
purified  samples  should  be  noted.  The  original,  at  the  moment 
of  incipient  boiling  with  the  Soldaini  reagent,  formed  a  heavy 
green  cloud,  while  with  the  purified  sugars  the  reagent  kept  its 
fresh  color  and  the  precipitate  was  only  noticed  when  filtered. 

The  United  States  Bureau  of  Standards  has  been  given 
samples  of  A,  B,  C,  and  D,  upon  which  it  is  conducting  tests. 
A  formal  report  of  these  has  not  yet  been  received.  It  will 
include  determinations  of  the  invert  sugar,  and  of  the  rotations, 
in  both  of  which  the  Bureau  is  making  every  effort  to  attain 
the  greatest  accuracy  at  present  possible.  A  preliminary  re- 
port1 on  the  tests  for  invert  sugar  has  been  received  in  which 
it  is  stated  that: 

Sample    A    contains    between    0.09%  &  0.08% 
B        "  "  0.02       &  0.01% 

C        "  "  0.02      &  0.01% 

D  less  than  0.01% 

The  relative  difference  between  B  and  C  is  about  0.003% 
and  between  C  and  D  is  0.005%.  A  comparison  of  these  deter- 
minations with  those  made  in  this  laboratory  will  show  that  the 
agreement  is  fairly  close  in  the  third  decimal  place. 

I  think  it  permissible  to  quote  from  the  informal  report, 
that  Sample  D  as  regards  invert  sugar  compares  very  favorably 
with  the  best  prepared  at  the  United  States  Bureau  of 
Standards. 

Freezing  Point  Lowering s. 

Dr.  Turner,  of  this  laboratory,  who  made  some  very  careful 
determinations  of  the  freezing  point  lowerings  of  normal  solu- 
tions of  each  sample,  has  kindly  allowed  me  to  publish  his 
final  averages.  The  details  of  his  work  will  be  published  later. 
The  following  molecular  lowerings  for  the  normal  solutions 
employed  are  accurate  +o.°ooi,  with  their  absolute,  but  not 
relative  values  subject  to  a  possible  slight  modification  when 
the  thermometer  is  still  more  carefully  calibrated. 
Sample  A  —2°. 037 

"  B      -2°.04I 

"          C      -2°.04I 

D    -2°. 048 

1  By   R.    F.   Jackson. 


A  slight  but  distinct  gain  in  the  molecular  lowerings  is  seen 
to  have  resulted.  That  this  occurred  in  spite  of  the  distinct 
lowering  in  the  content  of  invert  sugar  is  strange.  That  it 
could  be  due  to  alcohol  in  the  sugar  is  improbable,  because 
some  very  careful  tests  failed  to  reveal  any  indications  that 
alcohol  was  present,  and,  furthermore,  because  desiccation  in 
vacua  over  calcium  chlorid  gave  ample  opportunity  and  time 
for  the  removal  of  alcohol  before  the  freezing  point  determina- 
tions were  made.  One  consideration  to  which  great  import- 
ance is  not  attached  is  this.  Hot  methyl  alcohol  was  used  for 
the  final  washing  of  each  of  the  purified  samples.  According 
to  its  comparatively  greater  solubility  in  methyl  alcohol,  rani- 
nose,  a  normal  constituent  of  cane  sugar,  should  therefore  have 
been  rapidly  removed.  The  assumption  that  raffinose  of  higher 
molecular  weight  than  saccharose  was  rapidly  removed  by  the 
methyl  alcohol  is  in  harmony  with  the  observed  increase  in 
molecular  lowerings. 

A  summary  of  the  analyses  of  Sample  C,  the  stock  used  in 
the  measurements  of  osmotic  pressures,  is  now  given. 

%  Carbon  42.166 

'%  Hydrog-en 6.452 

f*  Invert  Sugar 0  01-0.02 

%Ash about  0.003 

Iron trace 

Calcium  none 

Alcohol none 

Normal  molecular  lowering-  of  freezing  point —2°. 041 

IMPROVEMENTS  IN  APPARATUS. 

The  apparatus  and  methods  used  at  this  laboratory  in  deten- 
mining  osmotic  pressures,  have  been  described  in  previous  pub- 
lications.1 A  few  minor  improvements  are  to  be  noted. 

Those  who  have  followed  the  work  will  recall  that  the  prin- 
ciple of  temperature  regulation  employed  is  to  pump  the  water 
rapidly  over  coils  of  pipe  kept  by  running  water  a  little  below 
the  temperature  desired  in  the  bath,  and  then  over  an  electric 
stove,  which  is  controlled  by  a  thermostat.  By  regulation  of 
the  thermostat  any  desired  temperature  may  be  maintained 
between  that  to  which  the  cooling  pipes  can  lower  the  water 
and  that  to  which  the  electric  stoves  can  warm  it.  The  air 
space  is  kept  at  constant  temperature  in  accordance  with  this 
same  principle,  a  fan  taking  the  place  of  the  pump,  and  an 
electric  light  serving  as  stove.  Because  of  the  different  heat 

1  Morse  &  Frazer,  Am.  Chem.  Jour.,  28,  1  ('02). 

Morse  &  Frazer,   Am.    Chem.   Jour.,   36.   1   ('05). 

Morse  &  Lovelace,   ibid,  40,  4   ('08). 

Morse  &  Mears,   ibid.  40,   3  ('08). 

Morse  &  Holland,   ibid,   41,   2   ('09). 


10 

capacities  of  air  and  water  and  the  different  volumes  of  each 
in  the  bath,  it  was  found  advantageous  to  separate  into  two 
sections  the  cooling  pipes  which  had  previously  been  in  series 
for  the  cooling  of  both  air  and  water  spaces.  Each  may  now 
be  separately  controlled.  Through  the  winter  months  the 
cooling  pipes  in  the  air  space  were  not  used  because  the  tem- 
perature of  the  outside  room  was  sufficiently  low  to  produce 
the  proper  cooling.  A  more  even  temperature  environment 
for  the  bath  was  furnished  by  the  installation  of  a  fan  in  the 
room  outside  the  bath.  Because  of'  the  relatively  low  heat 
capacity  of  air,  the  air  space  in  the  bath  is  the  more  difficult 
space  to  keep  at  constant  temperature,  but  it  can  be  done  with 
a  fair  degree  of  success  if  the  heating  and  cooling  sources  are 
nicely  adjusted  so  that  the  air  will  not  pass  over  either  an 
excessively  cool  or  an  excessively  warm  surface. 

For  the  maintenance  of  constant  temperature  we  are  of  course 
dependent  in  large  measure  upon  the  sensitiveness  of  the  mer- 
cury and  glass  thermostats.  The  least  sparking  of  these  will  cause 
fouling  of  the  mercury,  and  early  in  the  year  considerable 
trouble  was  definitely  traced  to  this  cause.  The  means  which 
had  been  used  to  prevent  this  was  the  spanning  of.  the  spark 
gap  by  the  proper  resistance,  either  that  of  a  75  volt  16  candle 
power  electric  light  filament,  or  that  of  graphite  painted  over 
a  porcelain  tube.  To  eliminate  the  sparking  altogether,  tin  foil 
condensers  are  now  used  to  span  the  spark  gaps.  Although  these 
tin  foil  condensers  alone  give  every  evidence  that  they  com- 
pletely absorb  the  induced  currents,  which  have  caused  spark- 
ing in  the  thermostats  at  the  "break,"  we  have  "made  assur- 
ance doubly  sure"  by  leaving  in  parallel  with  each  condenser  as 
a  "by  pass"  the  resistance  formerly  used  alone.  Several  ther- 
mostats which  have  been  used  in  various  baths  about  the 
laboratory,  have  worked  perfectly  since  their  spark  gaps  have 
been  "spanned"  with  these  condensers. 

It  has  been  noted  that  when  the  platinum  point  and  the  sur- 
face of  the  mercury  are  very  clean  the  mercury  will  wet  the 
platinum.  The  result  is  that,  when  the  thermostat  cools,  the 
mercury  still  clings  to  the  platinum  point,  and  the  breaking  of 
the  circuit  will  therefore  occur  at  a  slightly  lower  temperature 
than  the  "make."  This  is  easily  remedied  by  rubbing  the 
.finger  over  the  platinum  tip  until  it  is  found  that  the  platinum 
will  touch  and  leave  the  mercury  meniscus  sharply. 

After  these  two  sources  of  trouble  were  remedied  the  water 
space  kept  at  20°  for  a  period  of  two  months  at  a  stretch  to 
within  about  +  o°.oo5  except  at  three  observations,  when  the 
deviation  was  -fo°.oi,  due  to  stoppage  of  the  water  in  the 
cooling  pipes.  The  air  space  during  this  period  though  far 


II 

more  difficult  to  keep  constant,  did  so  with  only  an  occasional 
observed  deviation  of  +  o°.o5,  except,  of  course,  when  the 
bath  was  opened  to  change  the  cells. 

In  order  to  insure  constant  temperature  of  the  nitrogen 
volume  of  the  manometers,  it  seemed  desirable  to  eliminate  as 
far  as  possible  the  heating  effects  of  the  electric  light  used  in 
the  readings.  Accordingly,  a  device  was  made  by  which  the 
infra  red  waves  of  the  light  were  cut  off.  A  4%  solution  of 
nickel  sulfate  was  used  at  the  suggestion  of  Dr.  Pfund,  of 
the  Department  of  Physics,  and  this  was  enclosed  between 
glass  plates,  forming  a  screen  about  one  inch  thick.  An  eight 
candle  power  electric  light  bulb,  frosted  to  provide  a  soft,  dif- 
fused light,  was  placed  behind  this,  and  the  intensity  of  the 
illumination  increased  by  a  reflector  made  of  a  silvered  watch 
glass.  Tests  made  with  a  thermocouple  showed  that  the  ra- 
diant energy  emitted  through  the  nickel  sulfate  screen  was  but 
i%  of  that  given  by  the  unscreened  light.  The  green  color 
obtained  by  this  method  of  illumination  is  also  thought  to 
enhance  the  detail  of  both  mercury  meniscus  and  silvered 
meter  bar.  One  of  these  devices  has  been  used  in  the  deter- 
mination of  the  normal  volumes  of  the  manometers. 

THE  MEASUREMENTS— PRELIMINARY  DIS- 
CUSSION. 

Since  this  investigation  had  for  its  object  the  establishment 
of  one  link  in  the  chain  of  data  whereby  the  temperature  co- 
efficient of  osmotic  pressures  may  be  established,  relative 
rather  than  absolute  pressures  were  sought.  With  this  in  view 
the  technique  and  conditions  employed  in  measurements  at 
other  temperatures  were  followed  as  closely  as  possible. 

In  this  connection  attention  sfiould  be  called  to  two  well 
recognized  errors,  which  have  but  little  significance  in  the 
present  investigation,  but  which  render  the  data  somewhat 
inaccurate  for  the  comparison  of  high  with  low  pressures.  In 
our  manometer  data  the  volume  correction  in  calibration  units 
for  the  double  meniscus  is  taken  as  two-thirds  the  radius  of 
the  bore.  This  is  based  on  the  assumption  that  the  meniscus 
in  these  small  -bores,  of  about  half  a  millimeter  diameter,  is 
approximately  hemispherical.  Since  it  is  known  that  the 
meniscus  leaves  the  glass  even  in  capillaries  of  this  size  at  an 
angle  much  greater  than  zero,  and  since  actual  observation  of 
the  form  of  the  meniscus  shows  it  to  be  considerably  less  than 
hemispherical,  the  2/3r  correction  is  doubtless  too  large. 
With  low  pressures  the  error  will  be  insignificant,  but  when 
the  nitrogen  is  compressed  to  one  twenty-seventh  its  volume 


12 

under  standard  conditions  by  the  pressure  of  a  normal  solution, 
a  small  error  in  this  small  observed  volume  will  produce  a 
considerable  error  in  the  calculated  pressure.  It  would,  there- 
fore, be  unjust  to  claim  for  the  present  series  of  investigations 
great  accuracy  in  the  comparison  of  high  with  low  pressures 
for  the  purpose  of  substantiating  a  law  similar  to  Boyle's. 
But,  since  the  normal  volumes  of  the  manometers  are  of 
about  the  same  order  of  magnitude,  and,  since  they  are  com- 
pressed to  about  equal  degrees  for  the  same  concentration  of 
sugar  at  the  various  temperatures  employed,  the  error  is  of 
little  significance  in  the  purpose  of  the  present  series  of  meas- 
urements. 

The  second  error,  to  which  attention  was  called  in  1907,*  is 
one  which,  if  it  exists,  makes  the  data  inaccurate  for  the  com- 
parison of  high  with  low  pressures.  But  this  again  would  not 
alter  the  value  of  the  data  for  use  in  determining  the  tempera- 
ture coefficient  except  perhaps  by  an  indirect  effect  to  which 
attention  will  be  called  later.  The  error  lies  in  the  possibility 
that  the  membrane  formers  are  not  isosmotic.  If,  for  ex- 
ample, the  concentration  of  the  potassium  ferrocyanid  on  the 
interior  is  less  than  osmotically  equivalent  to  the  copper  sulfate 
on  the  exterior  of  the  membrane,  a  constant  positive  correction 
should  be  applied  in  order  to  obtain  the  true  osmotic  pressure 
of  the  cane  sugar.  Obviously  this  constant  correction  would 
be  of  greater  significance  to  the  low  than  to  the  high  pressures. 
But  an  example  will  show  that  this  error  would  have  to  be 
large  to  affect  the  sought  for  temperature  coefficient.  Let  us 
take  a  measurement  of  a  O.5N  solution  that  gave  an  observed 
osmotic  pressure  of  11.890  atmospheres  at  o°,  and  one  of  the 
same  concentration  that  gave  a  pressure  of  12.750  atmospheres 
at  20°.  The  "theoretical  gas  pressure"  of  such  a  solution  is 
11.133  atmospheres  at  o°,  and  11.950  at  20°.  The  ratio  of 
osmotic  to  gas  pressure  for  the  former  was  found  to  be  1.068 
and  for  the  latter  1.067.  Assume  now  that  the  potassium  fer- 
rocyanid and  copper  sulfate,  used  to  protect  the  membrane, 
differ  in  osmotic  pressure  by  as  much  as  — 0.03  atmposphere. 
Unless  the  potassium  ferrocyanid  itself  affects  the  osmotic 
pressure  of  the  cane  sugar,  we  are  justified  in  adding  this 
0.03  atmosphere  to  obtain  the  pressure  due  to  the  sugar  alone. 
We  then  obtain  as  the  corrected  pressures  11.920  at  zero,  and 
12.780  at  20°,  giving  for  the  ratio  at  zero  1.071  and  for  the 
ratio  at  20°,  1.070.  Each  ratio  is  considerably  changed  by 
this  correction,  but  each  by  the  same  amount,  so  far  as  the 
third  decimal  place  is  concerned,  and  hence  the  temperature 

1  Am.   Chem.   Jour.,   May,  1907. 


13 

coefficient  is  seen  to  have  remained  unaltered.  In  this  calcula- 
tion the  assumption  has  been  made  that  the  temperature  co- 
efficient of  dissociation  for  the  two  membrane  formers  are  prac- 
tically equal  in  the  range  of  temperature  used. 

Sources  of  error  which  would  render  the  measurements  in- 
accurate for  the  determination  of  the  temperature  coefficients 
have  not  been  overlooked.  A  change  of  temperature  in  the 
air  space  of  o°.i  will  not  affect  the  ratio  seriously,  and  can 
always  'be  allowed  for  in  the  calculation ;  but  a  similar  fluctua- 
tion in  temperature  in  the  water  space,  that  is  in  the  neighbor- 
hood of  the  cell  itself,  cannot  be  allowed  for  in  the  calculation, 
because  it  involves  the  expansion  or  contraction  of  cell,  solu- 
tion, brass  cone  and  collar,  and  the  mercury  in  the  bulbs  of 
the  -manometer.  It  has,  therefore,  been  our  practice  to  plug 
the  tops  of  the  cans,  into  which  the  cells  are  set,  with  cotton, 
so  that  any  change  of  temperature  in  the  air  space  could  only 
permeate  slowly  to  the  cell  and  the  bulbs  of  the  manometers. 
Of  the  two  hundred  and  eighty  observations  which  are  inclu- 
ded in  the  following  tables,  fourteen  were  made  when  the 
temperature  of  the  water  bath  varied  from  20°  more  than 
o.°  01,  and  in  but  two  was  the  variation  greater  than  o.°  03. 
The  variations  in  each  of  these  two  cases  was  o.°  3.  The 
maximum  probable  errors  in  weighing  the  solutions,  of  incli- 
nation of  the  manometers  to  the  meter  bar,  and  of  the  barom- 
etric readings,  could  only  affect  the  ratio  in  the  fourth  decimal 
place.  A  recent  calibration  of  the  meter  bar  used  with  the 
cathetometer,  shows  a  periodic  error  of  0.02  mm.  for  alternate 
millimeter  marks.  This  in  conjunction  with  the  unavoidable 
errors  in  reading,  may  have  affected  the  ratios  of  the  higher 
concentrations  to  a  very  slight  extent.  We  have  sought  to 
reduce  the  errors  of  reading  to  a  minimum,  both  by  check 
readings  by  two  or  more  observers,  and  by  keeping  ignorant  of 
the  figures  found  on  the  previous  observation.  The  agreement 
has  been  very  satisfactory.  In  checking  the  concentration  of 
the  solutions  before  and  after  the  measurements,  by  means 
of  the  saccharimeter,  the  agreement  of  different  observers,  and 
even  of  the  same  observer,  has  not  been  so  satisfactory.  After 
an  extended  series  of  comparative  readings  we  are  of  the  con- 
clusion that  for  a  solution  of  average  clearness,  darkened  as 
it  always  is  by  the  potassium  ferrocyanid,  o.i  point  on  the 
scale  of  our  Schimidt  and  Haensch  saccharimeter  is  the  limit 
of  our  accuracy.  When  the  difference  in  rotation  between  the 
solution  as  made  up  and  the  solution  at  the  close  of  an  experi- 
ment, both  compared  at  the  same  time  and  temperature,  was 
distinctly  as  great  as  o.i,  we  made  it  a  practice  to  discard  the 
measurement.  All  differences  less  than  this  are  recorded  as 


14 

"no  loss  in  rotation."  o.i  point  error  in  the  saccharimeter 
reading  corresponds  to  o.ooi  in  the  ratio  for  a  normal  solution, 
0.002  in  the  ratio  for  a  o.5n,  and  as  much  as  0.008  in  the  ratio 
for  a  o.i  normal  solution;  and  only  within  these  limits  are  the 
ratios  certain  to  be  unaffected  by  change  in  the  concentration 
of  the  solutions. 

We  have,  therefore,  taken  pains  to  prevent  the  dilution  or 
concentration  of  the  solution  which  inevitably  accompanies 
four  blunders  in  good  technique.  In  the  first  place,  the  cells 
before  being  set  up  are  filled  and  kept  in  thymol  water.  A 
thorough  rinsing  of  the  interior  with  the  sugar  solution  is 
therefore  necessary,  else  the  solution  will  become  diluted  by 
the  water  which  clings  to  the  interior  of  the  cell.  Secondly, 
the  solution  which  has  been  finally  poured  into  the  cell  will, 
in  exerting  its  osmotic  pressure,  cause  water  to  permeate  the 
membrane  with  resulting  dilution  of  the  solution,  unless  the 
manometer  is  quickly  fastened  in  place  and  an  initial  "mechan- 
ical pressure"  brought  to  bear  by  forcing  the  cone  down  into 
the  cell  so  that  the  osmotic  pressure  of  the  solution  is  balanced 
by  the  gas  pressure  in  the  manometer.  This  one  point  caused 
considerable  trouble  in  former  years,  when  the  means  of  secur- 
ing the  manometer  in  place  was  not  developed.  With  the  pres- 
ent arrangements,  and  "team"  work,  but  few  seconds  elapse 
between  the  time  when  the  solution  is  poured  into  the  cell  and 
the  moment  when,  with  the  manometer  firmly  secured,  the 
proper  initial  pressure  is  brought  to  bear  by  closing  the  exit 
tube  and  forcing  the  cone  down  by  screwing  up  the  brass  collar. 
Rapid  manipulation  is  also  essential  when  the  cell  is  taken 
down.  In  the  third  place,  this  initial  pressure  must  be  nicely 
adjusted  to  balance  the  probable  osmotic  pressure  to  be  devel- 
oped, since,  if  too  small  or  too  great  an  initial  pressure  is  given, 
the  solutions  will  be  diluted  or  concentrated  by  a  volume  of 
water  corresponding  to  the  volume  through  which  the  mercury 
in  the  manometer  must 'be  forced  in  order  to  establish  the 
equilibrium.  The  small  bore  of  the  manometer  allows  a  little 
range  in  this,  but  in  extreme  cases,  of  which  we  have  had  some 
examples,  concentration  of  the  solution  has  been  traced  to  the 
production  of  too  great  an  initial  pressure.  Such  cases  have 
confirmed  the  statement,1  "that  the  'mechanical'  pressure  upon 
the  solution  must  never  exceed  the  maximum  osmotic  pres- 
sure." Concentration  from  this  source  may  even  escape  de- 
tection because  of  the  operation  of  one  or  more  of  the  causes 
which  subsequently  produce  dilution,  and  is  consequently  to  be 
feared  more  than  dilution.  The  fourth  matter  to  which  atten- 

1  Am.    Chem.   Jour.,   Sept.,    1908,   p.   276. 


15 

tion  should  be  paid,  is  the  prevention  of  fluctuations  in  tem- 
perature just  after  the  cell  is  set  up.  The  cell  in  its  bottle  of 
o.in  CuSO4  is  immediately  placed  in  a  small  bath  at  the  proper 
temperature,  from  which  it  may  be  conveniently  removed  from 
time  to  time  for  the  adjustment  of  the  initial  pressure.  But 
the  manometer  projects  into  the  air  above,  which  is,  of  course, 
at  the  temperature  of  the  laboratory.  The  opening  of  a  win- 
dow, for  instance,  will  alter  the  temperature  of  the  nitrogen 
in  the  manometer,  and  it  becomes  troublesome  to  tell  its  pres- 
sure. We  have  been  favored  in  working  at  20°  by  the  ease 
with  which  it  is  possible  to  keep  the  laboratory  at  nearly  20° 
during  this  preliminary  manipulation. 

An  uncertainty  occurs  in  the  measurement  of  low  pressures 
bv  reason  of  the  fact  that  the  membrane  is  often  slow  in  allow- 
ing the  passage  of  sufficient  water  to  compensate  fluctuations 
in  barometric  pressure.  The  barometric  pressure  is,  of  course, 
subtracted  from  the  sum  of  the  pressures  of  nitrogen,  capillary 
depression  and  liquids  in  the  manometer  to  obtain  the  osmotic 
pressure.  If  the  barometric  pressure  suddenly  drops,  and  the 
membrane  is  slow  in  allowing  the  escape  of  sufficient  water  to 
compensate  for  this  drop,  the  observed  pressure  of  the  solution 
is  that  of  the  osmotic  pressure  plus  that  of  the  former  high 
barometer,  and  an  error  is  made  in  subtracting  the  new  low 
barometric  pressure.  This  uncertainty  is  often  evident  when 
measuring  the  lower  concentrations,  but  since  the  barometric 
pressure  is  small  in  relation  to  the  osmotic  pressure  of  high 
concentrations,  barometric  fluctuations  have  no  noticeable 
effect  upon  these. 

A  very  uncertain  source  of  error  lies  in  possible  variations 
in  the  bore  of  the  manometers,  and  the  consequent  variations 
in  the  capillary  depression  when  the  meniscus  is  at  different 
points.  This  error  also  enters  into  the  determination  'of  the 
normal  volume  of  a  manometer.  The  capillary  depression  of 
each  manometer  is  determined  experimentally,  but  only  for  one 
point.  From  an  inspection  of  the  calibration  curves  of  the 
manometers  the  bore  is  seen  to  vary  in  each  case,  but  it  is 
doubtful  whether  the  variations  are  of  sufficient  magnitude  to 
alter  the  capillary  depression  more  than  a  few  millimeters. 
This  is  a  matter  of  some  importance  to  determine  experimen- 
tally, and  it  will  be  made  the  subject  of  an  investigation  when 
accuracy  in  other  directions  becomes  sufficient  to  warrant  it. 
In  this  connection  attention  might  be  called  to  a  little  point 
where  care  has  been  used  in  the  present  investigation.  The 
lower  part  of  the  manometer  is  filled  with  solution  around  to 
the  first  bulb  where  it  meets  the  mercury.  If  care  is  not  taken 
to  have  the  mercury  in  this  bulb  at  the  widest  part  when  the 


i6 

final  pressure  is  developed,  and  the  surface  is  actually  near  the 
upper  constructed  part,  an  appreciable  capillary  depression  will 
obtain  which  is  not  allowed  for  in  the  calculations. 

In  accordance  with  the  usage  in  the  investigations  at  other 
temperatures,  the  capillary  depression  of  each  manometer  has 
been  reckoned  as  0.02  atmosphere.  As  experimentally  deter- 
mined, they  actually  range  from  0.015  to  0.023  atmosphere. 
Furthermore,  the  pressure  of  the  solution  measured  from  the 
surface  of  the  liquid  outside  the  membrane  to  its  height  at  the 
point  where  it  meets  the  mercury  in  the  manometer,  has  in  each 
case  been  taken  as  o.oi  atmosphere,  altho  it  varies  slightly  with 
each  manometer  and  with  the  density  of  the  solution.  By 
rounding  off  the  values  for  both  capillary  depression  and  pres- 
sure of  solution,  no  great  error  has  been  introduced,  but  the 
assumption  should  be  noted. 

It  is  to  be  regretted  that  more  measurements  which  fulfill 
the  requirements  to  be  mentioned  were  not  obtained.  That 
they  were  not  is  believed  to  be  due,  in  the  main,  to  two  causes. 
The  cells  available  for  the  measurements  had  been  used  at  o°, 
5°  and  10°,  and  it  has  been  observed,  almost  without  exception, 
that  cells  used  at  a  low  temperature  are  of  little  avail  for  meas- 
urements at  higher  temperatures  until  after  a  long  period  of 
treatment.  A  reason  for  this  will  be  mentioned  in  another 
connection.  The  cells  used  at  20°  were,  therefore,  not  in  prime 
condition  until  January,  and  indeed  there  is  some  evidence 
that,  in  spite  of  the  thymol,  the  slight  growths  of  Penicillium 
which  have  been  so  troublesome  in  the  past,  may  have  infected 
parts  of  the  cell  wall.  However  that  may  be,  by  January 
manometer  6  had  developed  a  flaw,  and  5  was  broken.  As 
subsequent  investigation  has  shown,  we  were  left  with  only 
one  reliable  manometer,  number  15,  and  possibly  21.  Since 
the  others  were  at  the  time  supposed  to  be  thoroughly  reliable, 
they  were  often  used  to  the  exclusion  of  15,  and  not  until  15 
was  used  continuously  and  9  came  upon  the  scene  late  in 
March,  were  reliable  measurements  obtained. 

The  criterions  which  the  measurements  have  been  required  to 
fulfill  in  all  the  series,  as  well  as  in  this,  before  they  were  ad- 
judged acceptable  were:  i.  Constancy  of  temperature  in  air 
and  water  spaces.  2.  Constancy  of  osmotic  pressure  for  a 
period  of  at  least  twenty-four  hours.  3.  No  change  in  the 
concentration  of  the  solution  that  could  be  detected  with  the 
saccharimeter.  4.  No  fault  which  could  be  detected  in  the 
technique  or  in  the  apparatus. 

Of  the  163  experiments  made  at  20°,  127  had  to  be  rejected 
as  not  fulfilling  one  or  more  of  the  above  requirements.  The 
remaining  36  are  recorded  in  the  following  tables. 


888888888888888 


-IA9Q 


•J  -Q 

•d  '0 

9SBJ9AY 


ggggggSSSgg 


•90U9J9jgiQ 


O  O  O 
ONGNOO 


'd  'O 


oofO 


•gou'B^sisg^ 


OOO'OO^oi^r-lOOOOOO 


O 
iO 


'IPO 


jo    - 


i8 


'HOISTS 


•SDiiajajfia 


r4  ,_(  ^  ,-t  r  » 

888888S8S 


o  o 

O  O 


o  o 

O  O 


r-i>io^o^i'-<<y>ONO 

xOfO'O'O^OOOCCOOO 
OOOOOOOO^t 


•3DU12}SIS92I 


'IPO 


Oit—  lr-1'O'O'Hr-I 

rovovor-io^^ 


0  o  «  o 


oo  o^  t^  01  ve  10  n  o 
r<  ci 


o  to  ^  vc  i 


odcddrH 


19 
TABLE  C. 


I 

.M. 

, 

» 

d 

fl 

.2 

I 

y 

u 

£ 

*  S 

1 

.2 

"rt 

rt 

H 

B 

•5  u 

.£  *o 

a 

a 

i 

'£  1 

C  B 

1 

0 

13  g 

o 

OTO 

O  'O 

.S  o 

fl 

flj 

jq 

_4 

C 

.^H      U 

•^  G 

X   V-* 

rt 

jo 

6  B 

0^ 

0 

"cd  ^ 

rt   0 

d  rt 

V 

5 

o 

5 

K 

& 

* 

5 

& 

0.1 

139 

t 

13 

1.050 

1.084 

.005 

.003 

72 

0.2 

148 

R 

20 

1.055 

.001 

.001 

24 

0.3 

151 

I 

20 

1.055 

.002 

.001 

47 

0.4 

91 

Y 

13 

1.042 

1.068 

.003 

.001 

45 

0.4 

93 

X 

13 

1.046 

1.071 

.001 

.001 

25 

0.5 

85 

P 

11 

1.049 

.001 

.001 

49 

0  5 

86 

O 

13 

1.045 

1.071 

.001 

.001 

49 

0.8 

105 

z 

24 

1.080 

1.101 

.002 

.001 

78 

0.9 

71 

H 

22 

1.072 

.002 

.001 

27 

0.9 

154 

F 

24 

1.096 

1.115 

.002 

.001 

72 

1.0 

118 

A5(63) 

24 

1.106 

1.124 

.003 

.001 

51 

THE   MEASUREMENTS   AND   THEIR   DISCUSSION. 

Table  A  is  a  summary  of  the  measurements  which  give 
ratios  agreeing  with  those  obtained  recently  at  o°,  5°,  and 
loV 

In  table  B  are  to  be  found  ratios  lying  between  those  obtained 
in  the  earlier  work  and  those  of  table  A. 

In  table  C  are  some  determinations  which  fulfill  all  the  re- 
quirements of  good  measurements,  except  that  a  curious  dis- 
crepancy in  the  volumes  of  the  manometers  occur,  which  at 
present  cannot  be  explained. 

The  columns  in  the  tables  are,  in  order,  the  concentration  of 
the  solution  in  terms  of  weight  normal,  the  number  of  the  ex- 
periment, the  date2  when  the  experiment  was  started,  the  cell 
used,  the  resistance  of  the  membrance  in  ohms  at  the  close  of 
the  electrolytic  renewal,  the  number  of  the  manometer,  its  vol- 
ume in  calibration  units  at  standard  conditions  of  temperature 
and  pressure,  the  average  observed  osmotic  pressure  in  atmos- 
pheres, the  theoretical  gas  pressure  in  atmospheres,  the  average 
difference  between  the  observed  osmotic  pressure  and  the  theo- 
retical gas  pressure,  the  average  ratio  of  osmotic  to  gas  pres- 


1  Dissertations  of  Zies  &  Gill,  15)09,  and   unpublished  work  at  10°   done 

in  1909. 

2  In  the  academic  year  1909-1910. 


20 

sure,  the  maximum  deviation  in  the  ratio  from  the  mean  of  all 
the  observations,  the  mean  deviation  of  the  same,- the  time 
period  in  hours  during  which  the  ratio  remained  constant. 

In  tables  A  and  B  only  those  measurements  are  included 
which  were  made  with  manometers  whose  volumes  at  standard 
conditions  of  temperature  and  pressure  were  determined  by 
the  side  tube  method  described  in  The  American  Chemical 
Journal  for  October,  1908.  It  will  be  seen  that  the  manometers 
in  table  C  are  an  entirely  different  set.  The  volumes  of  these 
latter  were  determined  by  comparison  with  a  standard  mano- 
meter. It  was  hoped,  that,  by  the  use  of  this  standard  mano- 
meter, the  normal  volumes  of  the  experimental  manometers 
could  be  calculated  by  employing  a  greater  range  of  pressure. 
Accordingly,  several  manometers  were  compared  with  the 
standard.  In  the  case  of  manometer  21  the  volume  as  calcu- 
lated by  comparison  with  the  standard  under  low  pressures 
agreed  very  well  with  the  volume  as  calculated  by  the  side  tube 
method.  At  pressures  of  from  three  to  seven  atmospheres 
however,  a  minimum  in  the  calculated  volumes  were  observed 
in  all  manometers  compared  with  the  standard,  and  at  higher 
pressures  the  calculated  volume  steadily  increased  with  increas- 
ing pressure. 

This  increase  is  probably  due  to  the  error  in  meniscus  cor- 
rection previously  mentioned ;  but,  since  neither  this,  nor  pos- 
sible causes  of  the  minimum,  have  as  yet  been  studied  quanti- 
tatively, the  proper  corrections  cannot  be  applied.  Obviously, 
the  only  course  to  pursue  at  present  is  to  bring  all  the  mano- 
meters to  a  comparable  basis  by  determining  their  normal  vol- 
umes by  one  method,  preferably  the  side  tube  method,  which 
is  an  absolute  one.  Unfortunately,  a  considerable  number  of 
measurements  were  made  with  manometers  n,  13,  20,  22  and 
24  before  there  was  an  opportunity  to  determine  their  normal 
volumes  by  the  side  tube  method.  When  13  and  24  were  so 
redetermined,  their  volumes  were  apparently  altered.  It  is 
impossible  to  say  at  present  to  what  the  discrepancy  is  due,  and 
consequently  the  ratios  of  table  C  cannot  be  placed  with  either 
those  of  table  A  or  B.  A  discussion  of  which  values  should 
be  taken  in  these  measurements  would  be  unprofitable  in  view 
of  the  total  uncertainty  attached  to  the  manometer  data.  Fur- 
thermore, in  certain  cases  the  results  are  vitiated  by  the  prob- 
ability that  the  wrong  volume  of  the  manometer  was  chosen 
as  the  basis  for  the  calculation  of  the  initial  "mechanical"  pres- 
sure, and  consequently,  a  concentration  of  the  solution  may 
have  occurred,  as  previously  shown  to  be  possible,  with  a  sub- 
sequent compensating  dilution,  and  the  saccharimeter  would 
have  indicated  no  change  in  concentration. 


21 

It  is  to  be  noted  that  the  high  ratios  agree  very  well  with 
those  found  at  o°,  5°,  and  10°  as  the  following  table  will  show: 

Weight    Normal    Concentration. 

0.1  0.2  0.3  0.4  0.5  0.6  0.7  0-8  0.9  1.0 

0°  1.061  1.059  1.061  1.069  1.076  1.084  1.094  1.104  1.115 

5«  1.082  1.083  1.059  1.061  1.067  1.074  1.084  1.093  1.101  1.115 

10°  1.08-3  1.061  1.061  1.066  1.072  1.083  1.092  1.102  1.114 

20°  1.083  1-061  1.062  1-059  1.067  1.073  1.083  1.091  1-103  .    ... 

mean     1.082       1.062       1.060       1.061        1.067       1.074       1.084       1.093       1.103       1.115 

The  ratios  in  table  B,  on  the  other  hand,  when  compared 
with  the  old  values  found  at  2O0,1  and  with  the  mean  values  of 
the  old  series  V  to  VIII,2  are  found  to  be  above  these  older 
values  in  each  case,  and  to  lie  between  the  lower  ratios  of  the 
older  series  and  the  higher  ratios  of  the  more  recent  investiga- 
tions. If  it  is  permissible  to  omit  experiment  29  simply  be- 
cause the  1.037  ratio  is  not  in  agreement  with  that  of  two  other 
measurements  of  the  same:  concentration,  the  relations  of  the 
ratios  in  table  B  to  the  mean  of  the  ratios  of  series  V  to  VIII 
and  to  the  mean  of  the  higher  ratios  given  in  the  above  table 
are  clearly  shown  in  the  plotted  curves. 

LOW   RATIOS    OF    FORMER    WORK    COMPARED    WITH    LOW    RATIOS 
FOUND    AT   20°    THIS    YEAR. 

Weight    Normal    Concentration. 
Series.  0.1        0.2        0.3        0.4        0-5  0-6        0-7        0.8        0-9        1.0 

VIII  20°  mean       1.055    1.051     1.038    1.042    1.045          1.060    1.066    1.077    1.084    1.093 
of  series. 

V-VIII  10°-25°      1.054     1  047     1.039     1.040     1-045          1.056     1.060    1-070    1-081     1.068 

Mean  ratios  in      1.057     1.050-56    1.064     1.081     1.089    1.100 

table  B. 

Perhaps  the  low  values  of  table  B  are  too  few  to  say  defi- 
nitely that  they  constitute  a  series  in  themselves,  but  the  pro- 
portionality between  them  is  striking. 

The  sharp  division  between  the  ratios  of  table  A  and  those 
of  table  B  calls  for  discussion.  The  search  for  possible  ex- 
planations will  be  found  to  be  met  with  difficulties  which  are 
insuperable  in  the  present  state  of  our  knowledge,  but  a  dis- 
cussion may  be  of  profit. 

At  first  thought  it  might  be  suspected  that  the  discrepan- 
cies were  due  to  the  use  of  different  manometers.  Manometer 
21  occurs  only  in  table  B  and  9  only  in  table  A.  9  is  not  sus- 
pected;  and  21  is  under  only  slight  suspicion  because  a  recent 
recalibration  indicates  a  slight  change  in  its  bore,  due  perhaps 
to  molecular  changes  in  the  glass.  The  curve  of  the  recalibra- 
tion has  been  used  in  the  calculations. 

Examining  the  dates  of  the  measurements  with  5,  6,  and  15, 
the  manometers  which  occur  in  both  tables,  we  find  that  the 


22 


one  low  value  with  5  occurred  after  four  high  values  were  ob- 
tained with  it,  while  four  low  values  with  15  were  obtained  be- 
fore the  six  high  values.  On  the  other  hand,  the  one  low 


I  fK> 


(   100 


0.3       Oij       0.)'       Oi,      0.7 


0.1        1.0 


HIGH    RATIOS     OBTAINED    IN     RECENT    WORK    COMPARED     WITH 
HIGH    RATIOS   AT  20°. 

value  obtained  with  manometer  6  has  its  date  sandwiched  be- 
tween those  of  the  two  high  values.  If,  in  subsequent  work,  it 
should  be  proved  that  the  manometers  need  more  frequent 


1  Morse  &  Holland,   Am.   Chera.   Jour.,  41,   4   (1900). 

2  Ibid,   page  275. 


23 

standardization  than  has  been  considered  necessary,  consid- 
erations such  as  the  above  may  be  of  value. 

Turning  now  to  the  cells,  it  is  seen  that  D  and  O  alone 
occur  in  both  tables.  It  would  be  unfair,  however,  to  attrib- 
ute great  significance  to  this,  for  an  examination  of  a  consider- 
able number  of  measurements,  which  were  rejected  only  be- 
cause of  a  slight  gain  or  loss  in  rotation,  shows  that  other  cells 
included  in  table  A  have  given  low  ratios  in  spite  of  gains  in  the 
rotation  of  the  solutions. 

We  might  find  in  the  conditions  or  known  errors  of  the  ex- 
periments some  constant  factor  which  will  explain  this  sharp 
division  in  the  ratios.  Let  us  inquire  if  any  such  factor  can 
be  discovered. 

It  has  been  suggested  that  the  low  pressures  might  be  due 
to  an  accumulation  of  copper  salts  in  the  cell  wall  during  the 
electrolytic  renewal  of  the  membrane.  Although  it  is  difficult 
to  see  how  this  should  affect  certain  measurements  always  to 
about  the  same  degree,  and  not  other  measurements  conducted 
under  apparently  the  same  conditions,  the  suggestion  was  taken 
as  the  basis  of  some  experimental  work.  A  cell,  after  subjec- 
tion to  the  customary  electrolytic  process  for  the  renewal  of 
the  membrane,  was  soaked  for  ten  days  in  frequent  changes  of 
water.  The  total  water  was  then  evaporated,  the  residue  of 
accumulated  thymol  ignited  and  evaporated  with  sulfuric  acid. 
The  residue  of  6  mg.  was  considered  as  that  of  CuSO4  soaked 
from  the  cell  wall.  Had  this  diffused  from  the  cell  wall,  and, 
by  very  slow  diffusion  contaminated  only  that  portion  of  the 
solution  adjacent  to  the  cell  wall,  it  might  have  had  a  slight 
effect  upon  /  the  observed  osmotic  pressure.  It  is  impossible, 
however,  to  say  what  its  distribution  would  have  been.  In 
some  cases  salts  may  diffuse  out  more  rapidly  than  in  others, 
while  it  is  perhaps  also  possible,  that  the  membrane,  which  in- 
advertently accumulates  on  the  cell's  exterior,  may  serve  in 
some  cases  to  retain  inclosed  salts  quite  completely. 

Another  cell,  after  the  customary  rinsing,  was  soaked  for  two 
hours  after  electrolysis,  the  time  usually  allowed  between  elec- 
trolysis and  the  setting  up  of  a  cell  for  a  measurement.  The 
residue  obtained  in  this  case  was  considerably  below  that  which 
can  be  estimated  by  ordinary  gravimetric  means. 

A  curious  fact,  with  which  this  idea  that  the  cell  wall  accu- 
mulates salt  has  been  connected  is  observed  when  a  cell  is  used 
more  or  less  continuously  without  giving  it  the  "rest"  and  the 
soaking  out,  which  has  become  a  regular  part  of  the  procedure. 
When  not  given  a  sufficient  "rest"  with  soaking,  cells  have  de- 
veloped constant  but  low  pressures.  A  notable  case  of  this  was 
observed  some  two  years  ago,  and  a  possible  explanation  is, 


24 

that  in  rushing  the  cells  into  frequent  measurements  the  re- 
peated electrolytic  renewal  of  the  membrane  plugged  the  cell 
wall  with  salts,  for  the  soaking  out  of  which  sufficient  time  was 
not  allowed.  In  the  present  investigation  each  cell  has  been 
soaked  about  a  week  between  measurements  made  with  it. 

Another  attempt  was  made  to  gain  an  experimental  basis  for 
the  supposed  influence  of  salts  accumulating  in,  and  diffusing 
out,  from  the  cell  wall.  It  has  been  found  best  to  renew  the 
membranes  in  o.in  CuSO4,  but  the  concentration  of  CuSO4 
used  as  membrane  former  in  a  measurement  is  o.oin.  It 
would  seem,  however,  that  if  the  membranes  were  renewed  in 
a  solution  of  the  same  low  concentration  as  that  into  which 
they  are  placed  during  a  measurement,  there  would  be  less 
chance  of  carrying  over  to  this  dilute  solution,  copper  sulfate 
which  might  have  accumulated  while  the  cell  was  in  the  more 
concentrated  solution  ordinarily  used.  This  was  tried,  but 
the  uncertainty  with  any  cell  is  so  great  that  no  conclusions  can 
be  drawn. 

Because  of  the  difficulty  of  drawing  conclusions  from  the 
data  obtained  in  any  of  these  methods  of  attack,  the  question 
was  investigated  directly  by  setting  up  cells  with  very  dilute 
solutions  and  open  manometers  capable  of  showing  very  slight 
differences  in  pressure,  the  plan  being  to  see  whether  any  dif- 
ference of  pressure  could  be  observed  between  cases  when 
every  chance  was  given  for  the  cells  to  lose  the  accumulated 
salt,  and  cases  when  the  cells  were  supposed  to  have  had  an 
opportunity  to  accumulate  salts  within  their  walls.  The  ex- 
periments though,  at  first  sight,  both  confirming  and  contra- 
dicting the  hypothesis  they  were  designed  to  test,  were  found 
to  be  so  involved  by  reason  of  some  unexpected  phenomena 
that  the  evidence  desired  can  only  be  untangled  after  further 
investigations. 

It  is,  of  course,  possible  that  a  minute  leak  in  the  membrane 
could  just  counterbalance  the  tendency  of  the  solution  to  de- 
velop a  maximum  pressure.  It  would  seem,  however,  that 
leaks,  even  if  they  allowed  constant  pressures  to  be  observed, 
would  cause  greater  divergence  in  the  results  obtained  in  dif- 
ferent instances.  Attention  is  called  to  the  agreement  between 
experiments  27  and  102  and  between  experiments  62  and  70. 
Furthermore  the  fact  that  a  very  careful  study  of  the  original 
and  final  solutions  with  the  saccharimeter  in  experiments  128 
and  102  showed  no  change  in  concentration  after  the  period  of 
89  hours  in  one  case,  and  16/j.1  hours  in  the  other,  argues 
against  leakage. 

1  The    maintenance    of    constant    pressures    for    periods    of    this    length 
would  seem  to  indicate  a  truly   semipermeable   membrane. 


25 

A  calculation  will  perhaps  bring  this  point  out  more  clearly. 
If  the  solution  should  leak  through  the  membrane  and  not  be 
replaced  by  water,  we  would  observe  a  steady  drop  of  the  mer- 
cury in  the  manometer.  In  the  case  of  two  o.Qn  measurements, 
both  made  with  manometer  15,  no  such  steady  drop  was  ob- 
served, and  the  actual  difference  between  the  observed  volume 
which  indicated  the  low  ratio  and  that  which  indicated  the  high 
ratio  was  only  0.3  calibration  unit,  or  about  0.06  cubic  milli- 
meter. It  is,  therefore,  necessary  to  assume  that  the  observed 
pressure  was  kept  constant  by  the  intake  of  sufficient  water  to 
replace  the  volume  of  solution  which  had  leaked  out.  Dilu- 
tion of  the  solution  must  therefore  have  occurred.  Now,  let 
us  say  that  10  milligrams  of  sugar  escaped,  and  the  solution 
containing  this  was  replaced  by  an  equal  volume  of  water.  The 
capacity  of  the  cell  is  about  20  c.c.  and,  had  twenty  c.c.  of  the 
o.Qn  solution  been  diluted  by  the  loss  of  10  milligrams  of  sugar, 
its  rotation  would  have  been  diminished  by  almost  0.2,  an 
easily  detected  loss.  But  let  us  assume  that  even  this  escaped 
detection,  and,  furthermore,  that  while  the  cell  was  quiet,  the 
dilution  only  occurred  in  the  fourth  of  the  total  20  c.c.  which 
lay  nearest  the  membrane.  This  5  c.c.  would  then  have  had 
its  sugar  content  reduced  from  the  original  1.5273  g.  to 
1.5173  g.1  The  observed  osmotic  pressure  of  the  first  concen- 
tration is  23.721  atmospheres,  and  of  the  second  would  be  about 
23.566  atmospheres,  a  difference  of  0.155  atmosphere.  The 
actual  difference  in  pressure  between  experiments  155  and  70 
was  0.306  atmosphere,  or  about  twice  the  amount  which  could 
be  accounted  for  when  every  advantage  is  given  to  the  above 
argument.  In  this  calculation  an  assumption  has  been  made 
which  is  perhaps  false  to  the  actual  phenomenon.  It  was  as- 
sumed that  the  observed  low  pressure  was  a  function  of  the 
dilution  of  the  solution.  A  pseudo  equilibrium  might  have 
obtained,  the  solution  leaking  out  with  extreme  slowness,  and 
the  water  entering  at  the  same  slow  compensating  rate.  The 
dilution  in  this  case  might  have  been  inappreciable  at  the  end  of 
even  a  considerable  period.  The  data  of  the  intake  of  water 
through  the  membranes  are  insufficient  to  base  any  calculations 
upon,  and  therefore  it  can  only  be  said  that  a  remarkably  exact 
and  constant  adjustment  of  intake  to  .leak  must  have  occurred 
in  each  case  to  produce  a  pseudo  equilibrium  of  the  constant 
magnitude  observed. 

Again,  if  the  original  solutions  were  wrongly  made  up,  the 
error  would  be  detected  in  the  rotation. 

Let  us  now  consider  another  point.     In  calling  attention  to 

1  The  error  in  assuming  the   weight  concentration  to  be  a  volume  con- 
centration is  negligible  in  this  calculation. 


26 

the  necessity  of  very  accurate  temperature  regulation,  Morse 
and  Holland  stated  in  their  article,  The  Regulation  of  Tempera- 
ture in  the  Measurement  of  Osmotic  Pressure /  that  "the  ideal 
would  be  a  regulation  so  exact  that  not  even  the  form  of  the 
mercury  meniscus  in  the  manometer  could  be  sensibly  affected 
by  variations  in  the  volume  of  the  inclosed  solution,"  and  " .  . .  . 
even  the  variation  in  the  form  of  the  meniscus  becomes  a  matter 
of  importance  whenever  it  is  attempted  to  measure  the  osmotic 
pressure  of  concentrated  solutions."  If,  for  example,  with 
manometer  15  and  the  pressure  of  a  0.911  solution,  the  observed 
volume  plus  the  double  meniscus  correction  is  22.57,  and, 
owing  to  slight  variations  in  temperature,  the  mercury  has 
risen  and  then  fallen  leaving  the  meniscus  flat,  then  one  half 
the  double  meniscus  correction  has  been  added  erroneously. 
One-half  the  double  meniscus  correction  for  manometer  15  is 
0.08  calibration  unit.  Subtracting  this  from  the  22.57  we  get 
for  the  true  volume  of  the  nitrogen  22.49  calibration  units. 
In  the  particular  observation  taken  as  the  basis  for  this  calcula- 
tion the  22.57  volume  was  found  to  give  a  ratio  of  1.090.  Had 
22.49  been  the  true  volume  it  would  have  given  in  the  calcula- 
tion a  ratio  of  1.094,  while  the  maximum  obtained  for  a  o.9n 
solution  is  1.103.  Obviously,  errors  in  meniscus  correction 
produce  the  greatest  effect  in  the  calculated  pressures  of  high 
concentrations,  and,  since  the  discrepancy  which  might  be  at- 
tributed to  a  complete  flattening  of  the  meniscus  effects  the  ratio 
for  a  o.9n  solution  but  four  points  in  the  third  decimal  place, 
as  shown,  it  would  have  proportionally  less  influence  upon  the 
ratios  for  lower  concentrations.  Further,  more  than  a  slight 
flattening  of  the  meniscus  would  not  have  escaped  notice  in  the 
reading.  Therefore  it  is  to  be  concluded  that  this  source  of 
error,  when  taken  alone,  is  insufficient  to  explain  the  differences 
between  the  ratios  of  table  A  and  those  of  table  B,  although  it 
is  of  considerable  import,  as  the  0.004  point  possible  error  in 
the  o.9n  ratio  will  show. 

It  is,  of  course,  possible  that  a  "heaping"  of  all  these  errors 
in  one  direction  could  cause  a  low  pressure  to  be  observed  in 
one  case,  while  the  maximum  was  allowed  to  develop  in  another 
case.  This  is  highly  improbable  in  view  of  the  fact  that  only 
one  distinctly  anomalous  value  has  been  observed.  There  is, 
therefore,  every  evidence  that  some  constant  difference  in  the 
conditions,  as  yet  not  fully  known,  has  caused  the  discrepancy. 
Certain  possible  sources  have  long  been  recognized ;  but  it  has 
been  the  policy  in  the  researches  in  this  laboratory  to  attack 
those  problems  which  seemed  of  greater  moment,  and  to  leave 

1  Am.    Chem.   Jour.,    Feb.,    1909. 


27 

other  smaller  sources  of  error  till  the  larger  ones  have  been 
removed.  At  present  our  time  and  thought  is  concentrated 
upon  the  manometers,  and  manometers  of  a  type  which  will,  for 
the  most  part,  eliminate  the  errors  of  meniscus  correction  are 
uriiier  construction.  With  the  development  of  these  and  other 
improvements  in  the  apparatus  the  time  is  approaching  when 
the  accuracy  of  the  measurements  will  exceed  even  that  which 
now  obtains,  and  the  absolute,  rather  than  the  relative,  osmotic 
pressures,  may  be  the  subject  of  future  investigations.  It  may 
therefore  be  well  to  call  attention  to  certain  conditions  which 
far  more  important  matters  have  forced  into  the  background 
to  await  more  thorough  investigation,  but  which  are  of  live  in- 
terest, not  only  because  they  are  recognized  as  having  a  possi- 
ble influence  upon  the  true  osmotic  pressure,  but  because  they 
may  possibly  have  had  something  to  do  with  the  discrepancies 
observed  in  the  present  investigation.  Because  of  the  scanti- 
ness of  quantitative  evidence  for  or  against  these  considera- 
tions, they  will  be  discussed  under  the  heading — 

THEORETICAL    CONSIDERATIONS. 

The  membrane  formers,  that  is  the  potassium  ferrocyanid, 
which  is  put  into  the  sugar  solution  and  the  copper  sulfate  into 
which  the  cell  is  placed  during  a  measurement,  were  calculated 
to  be  isosmotic  from  considerations  of  their  freezing  point 
lowerings  and  conductivities.1  The  concentration  of  osmotically 
active  particles  in  solutions  of  each  of  these  salts  at  the  dilu- 
tion used  is  still  in  doubt,  but  we  have  some  evidence  that  the 
solutions  in  use  as  membrane  formers  are  not  isosmotic.2  In 
addition  it  is  known,  that  there  is  a  considerable  difference  of 
potential,  when  a  potassium  ferrocyanid  solution  of  the  con- 
centration used  is  placed  in  the  cell,  and  the  cell  dipped  into  a 
copper  sulfate  solution  of  the  concentration  used  in  a  meas- 
urement. When  measured  with  platinum  electrodes,  by  a  po- 
tentiometer, and  at  constant  temperature,  the  two  solutions 
separated  by  the  membrane  of  cell  Z,  shortly  after  Z  was  taken 
down  from  a  measurement,  showed  a  difference  of  potential  of 
0.452  volts,  declining  to  0.449  volts  in  five  minutes.  With  cell 
P,  two  hours  after  it  had  been  subjected  to  the  electrolytic 
process  for  the  renewal  of  the  membrane,  the  difference  of 
potential  was  0.752  volts,  which  declined  steadily  to  0.519  volts 
at  the  end  of  three  hours.  In  each  case  the  electrode  in  the 
copper  solution  was  positive  to  that  in  the  ferrocyanid  solu- 
tion, as  might  be  expected  if  part  at  least  of  the  difference  in 

1  Am.    Chern.   Jour.,    34,   31;   34,  -311. 

2  Attention  was  called  to  the  significance  of  this  on  page 


28 

potential  is  due  to  the  establishment  of  a  liquid  element. 
The  curious  behavior  of  a  cell's  electrical  resistance  during  the 
round  of  its  treatment  is  also  to  be  noted.  When  treated  elec- 
trolytically  for  the  renewal  of  the  membrane,  the  resistance 
gradually  rises  in  the  course  of  an  hour  to  its  customary  max- 
mum,  which  for  some  cells  is  as  high  as  500,000  ohms,  and  has 
been  known  to  reach  1,000,000  ohms.  When  removed  from 
the  electrolizing  bath,  and  allowed  to  soak,  the  cell  is  found  to 
show  a  declining  resistance,  which,  in  the  course  of  a  few 
hours,  may  become  one-fifth  its  former  value;  and,  if  the  re- 
sistance is  taken  immediately  after  the  cell  has  been  taken  down 
from  a  measurement,  it  is  found  to  vary  considerably  in  dif- 
ferent cases,  and  in  certain  instances  to  be  close  to  the  initial 
resistance,  and  in  other  cases  to  have  declined  greatly.  * 

From  the  above  considerations  it  may  be  inferred  that  we 
may  possibly  have  to  deal,  not  only  with  a  difference  in  the 
osmotic  concentrations  of  the  two  membrane  formers,  but  also 
with  the  possibility  that  adjustments  towards  electrolytic  equi- 
librium may  take  place  in  varying  degrees.  It  is  to  be  hoped 
that  further  study  of  this  problem  may  throw  some  light  on  the 
discrepancies  observed  in  the  present  investigation. 

A  further  theoretical  consideration  is  now  presented,  not  be- 
cause any  great  importance  is  to  be  attached  to  a  certain  paral- 
lelism between  the  theory  and  certain  facts  which  have  become 
prominent  in  the  work,  but  because  it  is  hoped  that  the  idea 
may  be  of  interest. 

It  has  been  observed,  that  to  produce  a  membrane  capable  of 
allowing  the  development  of  a  maximum  osmotic  pressure, 
there  are  required  weeks  and  often  months,  during  which  the 
copper  ferrocyanid  membrane  is  repeatedly  packed  by  the 
electrolytic  process  using  as  high  a  potential1  as  is  consistent 
with  the  safety  of  the  membrane.  Weak  spots  in  the  mem- 
brane are  then  burst  by  subjecting  them  to  high  osmotic  pres- 
sure, with  the  membrane  formers  present,  and  the  rents  are 
mended  by  electrolysis.  Furthermore,  it  has  been  found  nec- 
essary to  renew  the  membrane  between  each  measurement. 
Membranes  which  have  not  been  so  repacked  just  previous  to 
a  measurement  have  been  found  not  to  allow  the  development 
of  the  highest  attained  pressures,  but  permit  a  steady  decline  in 
pressure.  At  times  a  new  cell  will  give  a  constant  pressure 
below  the  maximum,  but  never,  until  after  continued  treatment, 
a  maximum.  There  is  also  some  evidence,  obtained  this  year 
by  Dr.  Holland  and  Mr.  Meyers,  and  confirmed  by  past  expe- 
rience, that  the  efficiency  of  a  membrane  is  improved  when  it 


1.  110  volts  has  been  found  best. 


29 

is  packed  at  a  higher  temperature  than  that  at  which  the  meas- 
urement with  it  is  made,  the  supposition  being  that  the  coeffi- 
cients of  expansion  of  membrane  and  cell  wall  ace  such,  that, 
when  the  temperature  is  lowered,  the  membrane  is  packed 
closer.  There  is,  therefore,  some  basis  for  believing  that  the 
development  of  a  maximum  osmotic  pressure  is  intimately 
connected  with  a  close  texture  of  the  membrane. 

Let  us  now  assume  that  the  membrane  is  semipermeable  by 
reason  of  a  net-work  of  exceedingly  fine  capillaries.  Moore1 
on  the  basis  of  this  assumption,  deduces  the  following  relation 
connecting  the  surface  tension  of  solutions  with  their  osmotic 
pressure : 

(i.)  2HrT  =  nr2P 

whence  P  =  ^ 

"Where  T  is  the  difference  between  the  surface  tension  of 
the  solution  and  that  of  the  pure  solvent,  P  the  osmotic  pres- 
sure2 in  this  solution,  supposed  to  be  due  to  the  action  of  this 
difference  in  surface-tension,  and  r  the  radius  of  a  capillary 
opening,  placing  the  solution  and  the  solvent  in  communica- 
tion." 

According  to  the  equation,  P  =2r ,  P  is  a  function  of 
r  and  must  increase  as  r  diminishes ;  that  is,  as  the  membrane 
is  packed  closer  and  closer  and  the  capillaries  become  smaller 
and  smaller.  Moore  then  deduces  that  when  the  radius  of  the 
capillaries  become  so  small  that  the  surface  tension  acts  not 
only  at  the  perimeter  but  over  the'  whole  cross  section  of  a 
capillary,  a  condition  which  will  be  realized  when  the  diam- 
eter of  the  capillary  approaches  the  diameter  of  molecules, 
then  equation  (i)  becomes: 

n  r2 1  =  n  r2  P 

or  t=P 

where  t  is  the  difference  for  maximum  value  of  molecuar  at- 
traction for  solution  and  solvent.  Therefore,  with  capillaries 
of  molecular  dimensions,  the  osmotic  pressure  would  cease  to 
be  a  function  of  r  and  a  maximum  would  obtain. 

It  may  be  well  to  call  attention  to  the  fact  that  equation  ( i ) 
is  the  condition  of  a  pseudo  equilibrium.  According  to  well- 
known  thermodynamical  reasoning  P,  "the  osmotic  pressure" 
as  a  function  of  r  could  in  no  sense  of  the  word  be  taken  as 


1  Phil.  Mag.,  38,  279  (1894),  Fifth  Series. 

2  Referring  to  Moore's  article,   it  will  be   seen   that  less  danger  of  con- 

fusion would   have   been   incurred   had   P   been   termed   the  hydro- 
static  pressure. 


30 

the  true  osmotic  pressure  of  a  solution  in  equilibrium  with  the 
solvent. 

Attention  is  called  to  the  deduction  simply  to  show  the  in- 
teresting parallelism  between  what  it  suggests  to  the  mind,  and 
the  inference  which  is  aroused  by  a  consideration  of  the  meth- 
ods found  necessary  in  this  laboratory  to  produce  perfect 
membranes. 

In  conclusion  it  may  be  said,  that  no  one  of  the  considera- 
tions, experimental  or  theoretical,  which  have  been  advanced  in 
this  paper  can  be  claimed  in  the  present  state  of  our  knowl- 
edge to  be  adequate  for  the  explanation  of  the  discrepancy  be- 
tween the  two  sets  of  ratios ;  and,  with  one  -exception,  that  the 
constancy  of  the  discrepancy  is  such  as  to  seem  to  preclude 
the  argument  that  errors  were  "heaped."  Yet  all  considera- 
tions alike  seem  to  militate  against  the  low  and  in  defense  of 
the  high  values.  The  high  ratios  are  therefore  provisionally 
judged  to  be  the  more  reliable. 


SUMMARY. 

A  large  supply  of  cane  sugar  of  known  high  purity  has  been 
prepared,  in  order  that  the  measurements  in  progress  during 
the  past  year,  as  well  as  those  to  be  made  for  some  time  to  come, 
may  have  the  advantage  that  they  were  conducted  with  a  single 
stock  of  sugar  of  guaranteed  purity. 

Minor  improvements  have  been  made  in  the  apparatus 
used  at  20°. 

The  measurements  made  of  the  osmotic  pressures  of  cane 
sugar  solutions  at  20°  have  furnished,  on  the  one  hand,  data 
which  confirm  the  conclusion  deduced  from  measurements  at 
other  temperatures,  namely,  that  the  temperature  coefficient 
of  the  osmotic  pressure  of  cane  sugar  solutions  ranging  in  con- 
centration from  one  tenth  weight  normal  to  normal  follows 
closely  the  temperature  coefficient  of  gases  within  the  range  of 
temperature  o°-2O°. 

And,  on  the  other  hand,  there  have  accumulated  in  this  in- 
vestigation a  few  data  which,  if  taken  without  due  considera- 
tion, might  be  claimed  to  stand  at  slight  variance  with  the 
former  conclusion.  But  these,  it  is  believed,  are  of  more  scien- 
tific value  when  used  in  calling  attention  to  certain  conditions 
and  certain  problems,  which,  it  is  hoped,  further  investigation 
will  clarify  to  the  advantage  of  whatever  conclusions  the  evi- 
dence yet  to  be  accumulated  may  point. 


BIOGRAPHICAL. 

The  author  was  born  at  Tivoli-on-the-Hudson,  New  York, 
August  i /th,  1884.  He  prepared  for  college  at  the  Hotchkiss 
School,  Lakeville,  Connecticut.  He  received  his  A.  B.  at  Wil- 
liams College  with  the  class  of  1907,  and  the  year  after  grad- 
uation was  Assistant  in  Chemistry.  The  degree  of  Master  of 
Arts  was  conferred  upon  him  in  1908  by  Williams  College  for 
studies  in  Chemistry  and  Physics,  and  the  following  year  he 
entered  upon  his  work  for  the  degree  of  Doctor  of  Philosophy 
at  the  Johns  Hopkins  University,  with  Chemistry  as  major 
subject  and  Physical  Chemistry  and  Physics  as  subordinate 
studies.  He  has  held  a  University  Fellowship  during  the  aca- 
demic year  1909-1910. 


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